Window for a hot chamber that is sealed off from the surroundings

ABSTRACT

According to prior art, such windows are typically configured as a multiple glass pane module which is provided with at least two transparent glass panes ( 1, 2 ) that are held by means of distance pieces ( 3 ) in such a way that said panes are spaced apart. Said distance pieces are glued together with said panes ( 1, 2 ) in a gas-tight manner. The aim of the invention is to provide a gas pressure compensation between the inner chamber between the two panes ( 1, 2 ) and the surroundings without said panes getting dirty. According to the invention, the window is designed in such a way that at least one opening ( 5 ) is embodied in the distance pieces ( 3 ). Said opening is closed by means of a permeable filter ( 6 ) that enables gas to penetrate for pressure compensation but prevents steam and vapours to enter.

[0001] The invention is based on a window for a hot chamber sealed offfrom the surroundings, developed as a multi-pane module having at leasttwo transparent panes held apart by peripheral spacers, which panes areinterconnected with the spacers in gas-tight fashion.

[0002] Hot chambers that are sealed off from the surroundings and havehigh temperatures during operation typically have a window to allowviewing of the hot chamber from the outside. Depending on theapplication, the window can be permanently installed in the wallsbordering the hot chamber. In the case of a typical application,however, the window can also be integrated in a door of a wall borderingthe hot chamber. Typical examples of this are oven doors, such as doorsof ovens used for baking, in particular those with pyrolyticself-cleaning features, or microwave ovens.

[0003] Windows can also be provided in fire-proof doors that seal off achamber that becomes a hot chamber if fire breaks out.

[0004] Windows for the aforementioned purposes are typically developedas multi-pane modules having at least two glass panes held apart byspacers in a connecting frame.

[0005] A window of this type for an oven door is presented, for example,in DE 44 07 084 A 1 (=EP 0 731 318 B 1). The known window has a windowassembly having two glass panes arranged in a connecting frame, whichsaid panes form a glass pane interconnection, whereby this windowassembly is situated in the door with an empty layer of air separatingit from the front glass pane, forming the multi-pane module with saidfront glass pane. The glass pane interconnection—which itself isvapor-tight—is formed by a peripheral seal, in particular a glass fiberseal, that is effective even under the influence of heat, in order toprevent water vapor or steam from the oven muffle from entering thespace between the two glass panes of the window assembly and soiling thewindow. In order to keep such water vapor and steam away from the frontpane of the window as well, a peripheral flow barrier is also providedin the empty space between the front pane and the window assembly. Thisknown construction has the disadvantage in particular that thehermetically sealed, empty space between the glass panes of the windowassembly causes pressure to build, due to an increase in temperature,that significantly shortens the service life of the multi-pane module.

[0006] In order to compensate for this pressure increase, the knownconstruction according to DE 43 33 033 C 1 (=EP 0 646 753 B 1) providesa spacer developed as a compressible silicone tube, whereby the tubevolume makes pressure compensation possible when temperature changesoccur. The panes separated by the spacer are interconnected with eachother, together with the spacer, in hermetically-sealed fashion by meansof a temperature-resistant bonding agent, in particular a siliconebonding agent.

[0007] The glass pane exposed to the internal chamber temperature of theapparatus is typically composed of THERMAX 5000®, a prestressedsoda-lime float glass coated in heat-reflecting fashion, and the glasspane exposed to the ambient temperature and, if applicable, a furtherinternal intermediate pane, are composed of DURAX®, a prestressedsoda-lime float glass.

[0008] As a result of the compressible spacer, the distance between theglass panes depends on the temperature, because of which specialstructural requirements are placed on the design of the mechanicalholders of the glass panes, the interconnecting frame. Moreover, thespacer is continuously subjected to deformations, which does not have afavorable effect in terms of material fatigue.

[0009] A window for fire-retardant glass having a multi-pane module wasmade known in DE 36 37 064 C 2 in which the panes are held apart by asealing mass on the one hand and, on the other, are interconnected insealed fashion. This multi-pane module has a very expensive pressurecompensation system with valves that open in case of fire and releasethe gas pressure forming as a result of the temperature increase beforeit causes the panes to burst. Such a multi-pane module can also beprovided with a metallic frame at considerable production-engineeringexpense, whereby it has been made known in DE 39 15 687 C 2 to providethis module with an edge enclosure composed of a flexible, gas-permeableband.

[0010] An evacuated insulating glass composed of two panes having, e.g.,cylindrical, spacers between them distributed according to a certainpattern is also known. The edges of the glass panes are hermeticallysealed using either glass solder or metal solder in order to prevent airfrom entering. The distance between the panes is approximately 100 μm.

[0011] This multi-pane module has a number of disadvantages. Forinstance, thermally and/or chemically prestressed glass cannot be used,since the soldering temperatures are typically higher than therelaxation temperature of the prestressed glass. Moreover, the flatnessof thermally prestressed glasses has deviations that make it impossibleto realize the extremely close separations. Destressed glasses musteither have a thickness of min. 6 mm in order to withstand the vacuum,as a result of which the module becomes extremely heavy, or the spacerpattern must be configured so that it is sealed very tightly, whichmakes it difficult to look through. When special solders for lowsoldering temperatures are used, the seal is at risk of breaking duringuse. Additionally, it must be assumed that the panes will bend under thetemperature load and then touch each other; prevention of thermalconductance would no longer be ensured.

[0012] The invention is based on the object of developing the initiallydescribed window for a hot chamber that is sealed off from thesurroundings, designed as a multi-pane module having at least twotransparent panes held apart by peripheral spacers, which said panes areinterconnected in gas-tight fashion with the spacers, so that, despitethe gas-tight connection between the spacers and the panes, pressurecompensation can be obtained between the space between the panes and thesurroundings using simple means without allowing the windows to becomesoiled.

[0013] This object is attained according to the invention by the factthat at least one opening is developed in the spacers that is closedwith a permeable filter that allows gasses to penetrate for purposes ofpressure compensation, but prevents steam and water vapor from entering.

[0014] If increased pressure resulting from a temperature increasetherefore develops in the space between the panes, air can escape fromthe interior space via the filter. When the space between the panescools down again, filtered ambient air flows back into the intermediatespace. Any steam or water vapor is thereby deposited in the filter andis filtered out.

[0015] According to an embodiment of the invention, the filter istherefore advantageously designed to be replaceable. The filter ispreferably designed as a filter pad for this purpose.

[0016] According to an initial further development, the panes arepreferably made out of a glass having high thermal resistance, e.g., athermally and/or chemically prestressed borosilicate glass.

[0017] According to an alternative further development, the panes arecomposed of a glass ceramic that is highly temperature-resistant.

[0018] According to an advantageous embodiment of the invention, thespacers are preferably composed of stainless steel, aluminum, or asufficiently temperature-resistant plastic.

[0019] To obtain an interconnected assembly, the spacers are bonded withthe panes, according to an embodiment of the invention, using atemperature-resistant bonding agent, preferably a silicone bondingagent.

[0020] In order to obtain a further temperature reduction in the panefacing away from the hot chamber, the window according to the inventionis advantageously designed so that at least one of the panes is providedwith a thermal radiation-reflecting layer on at least one side.

[0021] The invention is described hereinbelow with reference to anexemplary embodiment shown in the drawings.

[0022]FIG. 1 is a schematic, perspective front view of an exemplaryembodiment of a multi-pane module having filters in the pane spacers,and

[0023]FIG. 2 is a cross-sectional view of the module according to FIG.1.

[0024] The exemplary embodiment of the multi-pane module, according tothe invention, of a window for a hot chamber that is sealed off from thesurroundings shown in FIGS. 1 and 2 has two transparent panes 1 and 2that are held in a not shown frame.

[0025] The panes 1 and 2 are composed of glass having high thermalresistance, typically a chemically or thermally prestressed borosilicateflat glass, or a transparent glass ceramic.

[0026] Both panes are held apart at a specified distance on theperiphery by spacers 3. The spacers are typically composed of stainlesssteel, aluminium, or a sufficiently temperature-resistant plastic.

[0027] The spacers 3 are bonded with the glass and/or glass ceramicpanes 1 and 2 using a temperature-stable bonding agent, typically asilicone bonding agent, to form an interconnection, which is indicatedin FIG. 2 by the bonding seam 4.

[0028] Moreover, the spacers 3 have bores 5 on at least one side of themodule, on the top side according to FIG. 1, and also on the lateralspacers according to FIG. 2. These bores 5 are filled with a filtermaterial 6 that slows the rate of gas exchange on the one hand, but alsoprevents pressure from building in the space between the two panes 1, 2and, on the other hand, also prevents penetration by water vapor in theform of grease, oil and other contaminating particles, which can soilthe space between the panes.

[0029] The multi-pane module “breathes”, so to speak, through the filterunit.

[0030] The panes 1, 2 are preferably coated in thermal-reflectingfashion, which is indicated in FIG. 2 by the position 7, whereby thelayers face each other when panes are coated on one side. Panes coatedon both sides can be used as well.

[0031] As a result of the invention, the main mechanisms of heattransmission: radiation (by an IR reflectance layer), convection (byreduced gas exchange), and conductance (by the use of poor heatconductors such as glass, ceramic, wood, plastics) can be eliminated insimple fashion, and the disadvantages of known systems do not occur.

[0032] The filter 6 is preferably developed as a filter pad so thefilter can be replaceable. The openings in the spacers that are closedby a filter are therefore formed preferably in the easily-accessiblearea of the spacers.

[0033] The multi-pane module according to the invention is used incombination with a front pane-installed with an intermediateseparation-in an oven door, preferably as a door assembly, whereby theempty space between the module and the front pane is advantageouslyventilated in order to keep the temperature of the front pane as low aspossible, even during the phase of pyrolytic self-cleaning.

What is claimed is:
 1. A window for a hot chamber that is sealed offfrom the surroundings, developed as a multi-pane module having at leasttwo transparent panes (1, 2) held apart by peripheral spacers (3), whichsaid panes are interconnected with the spacers in gas-tight fashion,wherein at least one opening (5) is developed in the spacers (3) that isclosed with a permeable filter (6) that allows gasses to penetrate forpurposes of pressure compensation, but prevents steam and water vaporfrom entering.
 2. The window according to claim 1, wherein the filter(6) is designed to be replaceable.
 3. The window according to claim 2,wherein the filter (6) is designed as a filter pad.
 4. The windowaccording to one of the claims 1 through 3, wherein the panes (1, 2) arecomposed of glass having high thermal resistance.
 5. The windowaccording to claim 4, wherein the glass is a thermally and/or chemicallyprestressed borosilicate flat glass.
 6. The window according to one ofthe claims 1 through 3, wherein the panes (1, 2) are composed oftransparent glass ceramic.
 7. The window according to one of the claims1 through 6, wherein the spacers (3) are composed of stainless steel,aluminum, or a sufficiently temperature-resistant plastic.
 8. The windowaccording to one of the claims 1 through 7, wherein the spacers (3) areadhesively bonded with the panes (1, 2) using a temperature-resistantbonding agent, preferably a silicone bonding agent.
 9. The windowaccording to one of the claims 1 through 8, wherein at least one of thepanes (1, 2) is provided with a thermal radiation-reflecting layer (7)on at least one side.